The XAllocClassHint function allocates and returns a pointer
to a XClassHint structure. Note that the pointer fields in the XClassHint
structure are initially set to NULL. If insufficient memory is available,
XAllocClassHint returns NULL. To free the memory allocated to this structure,
use XFree.

The XSetClassHint function sets the class hint for the specified
window. If the strings are not in the Host Portable Character Encoding,
the result is implementation-dependent.

XSetClassHint can generate BadAlloc
and BadWindow errors.

The XGetClassHint function returns the class
hint of the specified window to the members of the supplied structure. If
the data returned by the server is in the Latin Portable Character Encoding,
then the returned strings are in the Host Portable Character Encoding. Otherwise,
the result is implementation-dependent. It returns a nonzero status on success;
otherwise, it returns a zero status. To free res_name and res_class when
finished with the strings, use XFree on each individually.

The res_name member contains the application name, and the res_class
member contains the application class. Note that the name set in this property
may differ from the name set as WM_NAME. That is, WM_NAME specifies what
should be displayed in the title bar and, therefore, can contain temporal
information (for example, the name of a file currently in an editor's buffer).
On the other hand, the name specified as part of WM_CLASS is the formal
name of the application that should be used when retrieving the application's
resources from the resource database.